1. Field of the Invention
This invention relates to silane oligomers and more particularly to certain silane oligomers useful as dielectric fluids and/or anti-treeing additives for polymeric compositions.
2. Background of the Invention
Organosilanes have found wide use as lubricants, hydraulic fluids, coupling agents in mineral filled polymeric compositions, dielectric fluids, water repellants, tree retardant additives for polymeric electrical insulation and intermediates in preparing organopolysiloxanes.
For example, U.S. Pat. No. 2,559,342 of Burkhard discloses a family of hydrocarbyl alkoxyethoxy silanes prepared by reacting organochlorosilanes with alkoxyethanols. U.S. Pat. No. 3,814,691 of Csejka et al. utilizes organo silanes as a hydraulic fluid base stock. These silanes have the general formula: EQU (R[O--R"].sub.y O).sub.z --Si--R'.sub.4-z
wherein R is a C.sub.1 -C.sub.10 alkyl or a C.sub.6 -C.sub.10 aryl group, R' is a C.sub.1 -C.sub.4 alkyl group, R" is a C.sub.2 -C.sub.4 alkylene group, y is 1 to 5 and z is 1 to 3. U.S. Pat. No. 3,048,499 to Jellinek and U.S. Pat. No. 2,851,474 of Pines et al. disclose divinyldialkoxysilanes. British Pat. No. 953,421 discloses arylsilanes. U.S. Pat. No. 4,141,851 of Askew discloses silanes, useful in hydraulic fluids, having the formula ##STR2## wherein the most pertinent version of the broad general formula requires two Si--C bonds and two Si--O--C bonds on the single Si atom.
U.S. Pat. No. 4,172,806 discloses furfuryloxy substituted silanes, useful as dielectric fluids, of the general formula ##STR3## wherein R is selected from the group consisting of monovalent hydrocarbon radicals having from 1 to 10 carbon atoms, m has a value of 1 to 3, n has a value of 1 to 3 and m+n=4. Vinylfurfuryloxy substituted silanes are not specifically disclosed by Vincent nor their use as anti-treeing agents.
Polymeric compositions are well-known and are used extensively as insulation materials for wire and cable. As an insulator, it is important that the composition have various physical and electrical properties, such as resistance to mechanical cut-through, stress crack resistance and dielectric failure. Recent publications have indicated that water tree growth and elecyrical tree growth in the insulation are particularly important problems since they are associated with, though not necessarily totally responsible for, dielectric failure. The term "tree" has been applied to this type of insulation breakdown since the area of failure is a void space having the appearance of a tree foliage. Treeing usually is a slowly developing phenomenon and may take years to cause a failure in the insulation.
An important application for an insulation material is in high voltage transmission and distribution cable, especially in direct buried underground service. Two types of trees have been observed in these power cables, to wit, electrical trees and water trees, which are sometimes referred to as electrochemical trees. It is generally believed that electrical trees are generated by corona discharges causing fusion and breakdown of the polymer, whereas water trees are usually observed in cables buried in wet locations and have a different appearance compared to the electrical trees. Metal ions are usually found in water trees.
U.S. Pat. No. 4,144,202 of Ashcraft et al. relates to inhibiting the electrical breakdown or insulation by water treeing in dielectric materials based on ethylene polymers. As disclosed in the patent, water treeing is inhibited in the ethylene polymer compositions by employing therein organo silane compounds having an epoxy containing radical. German Offenlegungsschrift No. 2,737,430 discloses that certain alkoxysilanes added to polyolefin insulation prevent water-tree formation. Commonly assigned and copending U.S. patent application Ser. No. 161,932, filed June 23, 1980 discloses a number of organosilanes useful as tree retardant additives. Those particularly preferred contain at least one --OC.sub.2 H.sub.4 --O--R group where R is alkyl or aryl. Vinyltris(2-phenoxyethoxy)silane is specifically disclosed and exemplified as a useful water tree and electrical tree retardant for polymeric insulation.